The voltage output of an amplifier as a function of its input voltage is typically not linear over certain ranges of input voltages, particularly larger input voltages. Pre-distortion is a technique by which an input signal is pre-distorted in order to compensate for these non-linear ranges of an amplifier.
One of the goals of power amplifier design for wireless base-stations is increased efficiency. Improvements in efficiency can lead to a reduced amplifier cost (e.g. by allowing for the use of cheaper transistors with reduced power handling capability) and reduced operating expense (e.g. reduced size, reduced cooling requirements, reduced power requirements, etc.). In a conventional power amplifier, various techniques are often applied to class AB output stage configurations to achieve a desired level of performance, but the benefit of these techniques are limited in efficiency by the class AB output stage.
A multiple-path output stage, such as, for example, a so-called Doherty Amplifier, offers the potential of increased efficiency, but it is difficult to pre-distort the input so as to meet demanding wireless specifications of such an amplifier arrangement. Further efficiency enhancement can be achieved with an asymmetric Doherty amplifier (e.g. a Doherty amplifier arrangement where different technologies are used for the main and peaking amplifiers) but such an arrangement further increases the pre-distortion challenge.
Techniques of optimizing performance of a multiple path amplifier that overcome at least some of the above-noted deficiencies are highly desirable.